Allow HF in syscalls (#4119)

Author: shargon

src/Neo/SmartContract/ApplicationEngine.cs

@@ -274,7 +274,16 @@ protected static void OnSysCall(ExecutionEngine engine, Instruction instruction)
         {
             if (engine is ApplicationEngine app)
             {
-                app.OnSysCall(GetInteropDescriptor(instruction.TokenU32));
+                var interop = GetInteropDescriptor(instruction.TokenU32);
+
+                if (interop?.Hardfork != null && !app.IsHardforkEnabled(interop.Hardfork.Value))
+                {
+                    // The syscall is not active
+
+                    throw new KeyNotFoundException();
+                }
+
+                app.OnSysCall(interop);
             }
             else
             {
@@ -691,19 +700,20 @@ private static Block CreateDummyBlock(IReadOnlyStore snapshot, ProtocolSettings
             };
         }
 
-        private static InteropDescriptor Register(string name, string handler, long fixedPrice, CallFlags requiredCallFlags)
+        private static InteropDescriptor Register(string name, string handler, long fixedPrice, CallFlags requiredCallFlags, Hardfork? hardfork = null)
         {
             var flags = BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Static;
-            MethodInfo method = typeof(ApplicationEngine).GetMethod(handler, flags)
+            var method = typeof(ApplicationEngine).GetMethod(handler, flags)
                 ?? typeof(ApplicationEngine).GetProperty(handler, flags).GetMethod;
-            InteropDescriptor descriptor = new()
+            var descriptor = new InteropDescriptor()
             {
                 Name = name,
                 Handler = method,
+                Hardfork = hardfork,
                 FixedPrice = fixedPrice,
                 RequiredCallFlags = requiredCallFlags
             };
-            services ??= new Dictionary<uint, InteropDescriptor>();
+            services ??= [];
             services.Add(descriptor.Hash, descriptor);
             return descriptor;
         }

src/Neo/SmartContract/InteropDescriptor.cs

@@ -58,6 +58,11 @@ public uint Hash
         /// </summary>
         public long FixedPrice { get; init; }
 
+        /// <summary>
+        /// Required Hardfork to be active.
+        /// </summary>
+        public Hardfork? Hardfork { get; init; }
+
         /// <summary>
         /// The required <see cref="CallFlags"/> for the interoperable service.
         /// </summary>